Downhole logging systems have been used for many years to evaluate the characteristics of the wellbore, including the liquid-gas fraction of fluids in the wellbore and the lithology of the surrounding geologic formations. Induced gamma ray radiation has been used in many prior art logging systems. Such downhole monitoring tools are provided with a gamma ray emitter that includes a low-energy radioisotope (e.g., Americium-241) and a gamma ray detector. The extent to which the emitted gamma rays are attenuated or back scattered before reaching the detector provides an indication of the bulk density of the wellbore fluid and formations surrounding the monitoring tool. Scintillation detectors are also used to detector and report neutron radiation.
Prior art nuclear detectors include a scintillator and vacuum photomultiplier tube. The scintillator emits light in response to gamma ray radiation. The vacuum photomultiplier tube (PMT) converts the light emitted from the scintillator into an electric signal that is representative of the incident gamma ray radiation. The scintillator is retained within the housing of the detector assembly with a metal sleeve. The scintillator may include a reflector that directs light emitted from the scintillator to the photocathode of the photomultiplier tube housing through a sapphire or quartz window.
Although widely accepted, current scintillator detector designs are complicated, difficult to manufacture and susceptible to failure when exposed to elevated temperatures or mechanical shock. There is, therefore, a continued need for a scintillator detector that overcomes these deficiencies in the current state of the art. It is to this and other needs that the preferred embodiments are directed.